I attempted to test this at your site, but it appears that you've disabled it.
It's enabled under Guest user group and under Display > General > Captcha Settings.
There were a couple spam bots that got by the captcha when it was working, but I haven't changed anything with it as far as I know...
There are 18 errors on the front page though using Chrome Developer Mode, but don't really see any regarding ReCaptcha...